Method and devices for identifying a vehicle using a location

ABSTRACT

Methods for identifying a vehicle using a predetermined location, and a radio beacon and an onboard unit are provided. One method comprises: carrying, on the vehicle, an onboard unit that broadcasts status messages that each indicate a current relative distance of the onboard unit from the predetermined location and a radio identifier that changes after each or several status messages; receiving at least one status message in a radio beacon; detecting a location usage of the vehicle by evaluating the status message(s) based on the indicated relative distance; transmitting an identification request from the radio beacon to the onboard unit addressed according to the radio identifier from the status message(s); receiving and conducting a legitimacy check of the identification request in the onboard unit; and if the request is legitimate, transmitting an identification of the onboard unit to the radio beacon that remains the same over changes of radio identifier.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to European Patent Application No. 12 166 502.0, filed on May 3, 2012, and to European Patent Application No. 13 158 877.4, filed on Mar. 13, 2013, which are both incorporated by reference herein in their entireties.

BACKGROUND

1. Technical Field

The present application relates to a method for identifying a vehicle using a predetermined location, and further relates to a radio beacon and to an onboard unit for use with the method.

2. Background Art

Methods for identifying vehicles are required, for example, so as record, monitor, authorize and/or impose tolls (charge fees) for the usage of locations by vehicles. Such usages of locations can, for example, include the entering of areas to which access is limited or that are monitored, a fee-based stay at a particular location, for example a parking lot that is subject to a charge, or the use of traffic routes subject to tolls, such as highways or inner cities (city toll), and the like. According to known vehicle identification methods, license plate numbers (registration plates) are read by way of optical character recognition (OCR), or the vehicles are equipped with onboard units (OBUs) having a unique identification, which can be read out via a radio interface such as dedicated short range communication (DSRC), radio frequency identification (RFID), wireless local area network (WLAN), wireless access for vehicular environments (WAVE), or the like.

So as to create a clear association of a wirelessly read OBU identification with the location used by the vehicle, presently radio beacons, which are used for wireless reading, are mounted on special installations (“gantries”) at the location to be monitored and equipped with narrowly defined radio coverage ranges. Alternatively, satellite navigation-based onboard units are employed that transmit the self-located position data via a mobile communication network to a back office, which performs a map matching with the locations to be monitored. All of these known methods require not only special, complex installations, both in the vehicle and on the road, but also disclose the identity of the OBU (in the form of a wirelessly read OBU identification), even if no location usage requiring monitoring exists, which is objectionable for data protection reasons.

BRIEF SUMMARY

It is one object to create methods and devices that allow vehicles using a location to be identified in a simpler manner and with improved confidentiality for uninvolved vehicles.

This object is achieved in a first aspect by a method, comprising: carrying, on the vehicle, an onboard unit that via radio repeatedly broadcasts status messages, which each indicate a current relative distance of the onboard unit from the predetermined location and a radio identifier that changes after each or several status messages; receiving at least one status message in a radio beacon; detecting a location usage of the vehicle by evaluating the at least one status message based on the relative distance indicated therein; transmitting an identification request from the radio beacon to that onboard unit which is addressed by way of the radio identifier from the at least one status message; receiving and conducting a legitimacy check of the identification request in the onboard unit; and, if the request is legitimate, transmitting a unique identification of the onboard unit to the radio beacon, the unique identification remaining the same over several changes of radio identifier.

An aspect is based on a novel integration of onboard units transmitting status messages, such as those known, for example, from the ITS-G5 or WAVE (IEEE 802.11p) standards, in the form of common awareness messages (CAM) or basic safety messages (BSM). The messages are emitted as repeated broadcasts so as to warn or notify neighboring onboard units or roadside infrastructure in order to avoid collisions or provide the driver with an improved overview of the situation. So as to render the creation of movement profiles of a vehicle more difficult, the status messages are sent only under temporary radio identifiers, which change from time to time and are not known to the system operators, so as to protect the privacy. Only the temporary radio identifiers of at least one status message of the onboard units are evaluated. Only after the usage of the location has been detected—anonymously as a result of the temporary radio identifiers—is the onboard unit requested to reveal the “true” identity thereof, for example payment, use or application identity. This ensures that in fact only those onboard units are identified, which used the predetermined location; onboard units of third-party vehicles, which merely pass the location in the vicinity or turn around just before actual usage of the location, and the like, are not identified, which is to say they remain anonymous. Consequently, high data protection requirements in terms of privacy can be satisfied, without necessitating complex road-side installations, OBU modifications or separate anonymization devices such as proxy computers.

The measure, according to which each onboard unit itself calculates the relative distance thereof from the predetermined location and transmits the finished calculation result to the radio beacon, relieves the unit of the computationally intensive calculation of the distance. All the radio beacon is now required to do is to evaluate the relative distances, for example check them to see whether a drop below a predetermined maximum distance has occurred, so as to detect the location usage based thereon.

According to a first embodiment, information about the predetermined location is transmitted from the radio beacon to the onboard unit, which then based thereon and based on its current position calculates the relative distance.

As an alternative, information about the predetermined location can be stored in the onboard unit, which based thereon and based on its current position calculates the relative distance. For example, each onboard unit can include lists of installation locations of radio beacons as predetermined locations, have previously stored them, or received them via radio, for example distributed by radio beacons, and can use these lists so as to determine the relative distance from the respective nearest radio beacon.

In another embodiment, at least two status messages are received in a radio beacon and are associated with each other based on the radio identifiers indicated therein, and the location usage by the vehicle is detected by evaluating the mutually associated status messages based on the relative distances indicated therein.

By mutually associating and evaluating at least two status messages, an onboard unit is tracked over a short period of time, which is sufficient to be able to establish the usage of a particular location with high certainty. Even two or just a few status messages that can be associated with one and the same onboard unit may suffice for this purpose to exclude measurement errors and reliably detect a movement that has occurred with respect to an increasing or decreasing relative distance. In the simplest case, such a detected location usage can be the crossing of a predetermined boundary around the predetermined location, if the first status message indicates a relative distance outside the boundary and the second status message indicates a relative distance inside the boundary, so as to detect a location usage.

According to another aspect, the legitimacy check is carried out by checking a cryptographic sender certificate of the radio beacon that is transmitted by the radio beacon along with the identification request. The onboard unit thus discloses the identity thereof only to identified, legitimate inquirers, which further improves the protection of privacy.

For the same reason, it may be advantageous for the identification of the onboard unit to be transmitted to the radio beacon via an encrypted channel. Direct (point-to-point) encrypted communication can be established between the onboard unit and inquiring radio beacon for this purpose. For example, the encrypted communication channel can be part of the protocol at the radio interface between the onboard unit and the radio beacon, for example part of the ITS-G5 or WAVE standard, but alternatively could also be established separately via a 3G, 4G or 5G mobile communication network.

In an application of an identification method, the identification received in the radio beacon is recorded together with a time stamp in a memory so as to log the location usage, for example for monitoring purposes.

In an alternative application, the identification received in the radio beacon is compared to at least one previously stored legitimate identification so as to authorize the location usage, for example so as to open gates, lower a wheel lock, deactivate an enforcement system or the like.

In another application of the identification method, the identification received in the radio beacon is used to search for and debit a toll account associated with the identification, so as to toll the location usage, for example so as to levy a location and/or time toll, parking fees, road usage fees, city toll or the like.

In all three variants, the radio beacon can transmit a beacon identifier that is unique to the radio beacon to the onboard unit after logging, authorization or tolling of the location usage, the onboard unit storing this identifier and transmitting the same along with the next broadcast of the status message(s) thereof or transmission of the identification thereof, and the radio beacon can ignore a status message or identification received from an onboard unit, if the beacon identifier received along therewith is identical to its own beacon identifier. Inadvertent double logging, authorization or tolling of one and the same onboard unit in the radio coverage range of a radio beacon can thus be prevented.

According to a further characteristic, more than two status messages can be received and associated with each other, and a movement trend of the onboard unit can be calculated based on the relative distances indicated in these messages, the trend being compared to the predetermined location so as to detect the location usage. This allows the detection reliability to be increased and, for example, “measurement outliers” to be better suppressed.

It may be advantageous if the respective radio identifier is changed after approximately 5 to 1000, including being changed after 20 to 100, status messages. The more frequently the radio identifier changes, the greater is the data protection in terms of the traceability of a particular onboard unit; the less frequently the radio identifier changes, the lower is the risk that the radio identifier around the location to be detected changes, which would make detection more difficult. The values indicated above constitute a good compromise between these mutually opposing requirements.

As an alternative, the change interval of the radio identifier of the onboard unit can also be set so that the radio identifier is changed at the earliest after expiration of a predetermined time period. Based on the size of a customary radio coverage range of a radio beacon and an average speed of onboard units, the predetermined time period can be selected so that no radio identifier change takes place with high certainty when an onboard unit passes a radio beacon.

Another aspect is to keep the radio identifier the same while the onboard unit is located in the radio coverage range of one and the same radio beacon. For this purpose, for example, the onboard unit can directly measure the radio coverage range of a radio beacon if the radio beacon periodically broadcasts beacon identifiers, or can determine the same based on previously stored lists or maps of radio coverage ranges of known radio beacons, or be notified by a radio beacon as part of one of the broadcasts or the identification request of the beacon.

The status messages can further also contain the current position and/or a current movement vector of the onboard unit, which is or are used along with the detection of the location usage so as to further increase the detection reliability.

According to a further characteristic, the current position of the onboard unit can be determined by way of satellite navigation and improved by referencing to a reference position of the radio beacon that was determined by way of satellite navigation, in the manner of differential GPS (dGPS), wherein the radio beacon forms the reference receiver so as to improve the positions of the onboard units determined by way of satellite navigation.

As an alternative, the current position of the onboard unit can be determined by way of satellite navigation and improved by referencing to at least one further position of a neighboring onboard unit that was determined by way of satellite navigation. This embodiment is based on the assumption that, given the proximity to each other, the onboard units that are present in the radio coverage range of a radio beacon are each subject to the same satellite navigation errors and neighboring OBUs thus can be used as comparison receivers in the manner of dGPS.

In general, a radio beacon may be used to detect location usages in the immediate or wider environment thereof, or even in remote territories outside the radio coverage range thereof; however, the radio coverage range of the radio beacon may contain the predetermined location, so that each radio beacon is in charge of location usages in the immediate surroundings thereof and thus receives current and local measurement data from onboard units.

In a second aspect, a radio beacon is created for identifying a vehicle using a predetermined location, the vehicle carrying an onboard unit that via radio repeatedly broadcasts status messages, which each indicate a current relative distance of the onboard unit from the indicated location and a radio identifier that changes after each or several status messages, wherein the radio beacon is configured to, with the aid of a processor and a transceiver connected thereto: receive at least one status message; detect a location usage by evaluating the at least one status message based on the relative distance predetermined therein; transmit an identification request to that onboard unit which is addressed by way of the radio identifier from the at least one status message; and receive a unique identification of the onboard unit that remains the same over several radio identifier changes.

In an aspect, the radio beacon may be configured to receive at least two status messages and associate these with each other based on the radio identifiers indicated therein, and detect the location usage of the vehicle by evaluating the mutually associated status messages based on the relative distances indicated therein.

The radio beacon may contain a cryptographic sender certificate and is configured to transmit the same along with the identification request.

In a third aspect, an onboard unit is created, comprising a processor, a satellite navigation receiver for position determination, and a transceiver for radio communication. The onboard unit is configured to: repeatedly broadcast status messages via radio using the transceiver, each message containing a radio identifier of the onboard unit that changes after several status messages; wherein the onboard unit is further configured to indicate in each status message the current relative distance thereof from a predetermined location, as determined by way of the satellite navigation receiver; receive an identification request from a radio beacon, the request being addressed to the current radio identifier of the unit and containing a cryptographic sender certificate; validate the sender certificate; and if the sender certificate is valid, transmit a unique identification of the onboard unit to the radio beacon, the identification remaining the same over several radio identifier changes.

The status messages of the onboard unit may be modified CAMs according to the ITS-G5 standard or modified BSMs according to the WAVE standard.

Further features and advantages, as well as the structure and operation of various embodiments, are described in detail below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

With regard to additional characteristics and advantages of the radio beacon and onboard unit, reference is made to the above descriptions of the method, and the description below of embodiments, which is provided referencing the accompanying drawings, in which:

FIG. 1 shows a schematic overview of components, including the radio beacon and several onboard units, acting according to an example method embodiment.

FIG. 2 shows a block diagram and a signal flow chart of a method, according to an example embodiment.

FIG. 3 shows a sequence diagram of the exchange of messages at the radio interface between the radio beacon and onboard unit, according to an example embodiment.

Embodiments will now be described with reference to the accompanying drawings.

DETAILED DESCRIPTION

FIG. 1 shows a road toll system 1 as an exemplary application of the identification method, comprising a back office 2 and a plurality of geographically distributed roadside radio beacons (roadside entities, RSE) 3 that are connected thereto. Each of the radio beacons 3 has a limited radio coverage range 4, for example a wireless radius of 200 meters, within which predetermined locations such as points 5 (“virtual toll plazas”), areas 6 (for example parking lots), boundaries 7 (for example virtual gantries, inner city boundaries or the like) or road segments 8 are defined, wherein the locations 5-8 can also be entirely or partially located outside the radio coverage range 4. They may be located (at least partially) inside the radio coverage range 5, which simplifies the association of a radio beacon 3 with the locations 5-8 for which the beacon is in charge.

The radio beacons 3 detect location usages of vehicles 9 that pass the radio coverage range 4 of the beacons, which is to say whether—and optionally how long—these use one of the locations 5-8, and identify such vehicles 9 that use the locations. Vehicles 9 that do not use any of the locations 5-8 are not to be identified, which is to say remain anonymous.

For the purposes mentioned above, all vehicles 9 are equipped with onboard units (OBUs) 10, the configuration of which will be described in more detail based on FIG. 2.

According to FIG. 2, each OBU 10 comprises a satellite navigation receiver 11 for successively repeated determining the respective current position (“position fix” P₁, P₂, . . . , P_(i) in general, of the unit in a global satellite navigation system (GNSS) such as GPS, GLONASS, Galileo or the like. Moreover, the OBU 10 is equipped with a processor 12 and a transceiver 13, wherein some of the data connections between the satellite navigation receiver 11, processor 12 and transceiver 13 are not shown for clarity reasons.

Reference numeral 14 schematically denotes a service application that can be executed by the processor 12, for example a toll application, which can cooperate with the radio beacons 3 and the back office 2 of the road toll system 1 in a manner that will be described hereafter and for this purpose has an OBU identifier uID that is unique (“unique ID”) in the road toll system 1. For example, the OBU identification uID can be a unique production identifier of the OBU 10, the name of the owner thereof, the name of the owner of the vehicle on which the OBU 10 is mounted, an account or credit card identifier of the vehicle owner or the like. In the road toll system 1, the OBU identification uID is known to the back office 2 and/or the radio beacons 3 and can be used there for identifying the vehicle 9 that carries the OBU.

Reference numeral 15 denotes a security application which is processed by the processor 12 and by way of which the OBU 10 successively and repeatedly, for example periodically approximately every 100 ms, broadcasts a status message 16 via the transceiver 13. The status message 16 is intended to be received by OBUs 10 of neighboring vehicles 9 and/or roadside infrastructure, such as the radio beacons 3, and requires neither a confirmation of receipt nor actual receipt; the application 15 transmits status messages 16 via the transceiver 13 regardless of whether or not these are received by a receiver, however optionally the application can also be requested to do so by radio beacons 3 or other OBUs 10.

Each of the status messages 16 can include the last position P, of the OBU 10 as determined by way of the satellite navigation receiver 11, and optionally additional data, for example the speed and direction of movement (movement vector) M, height, measurement accuracy, and the like. Each status message 16 is provided with a temporary radio identifier pID, so that neighboring OBUs or infrastructure can correlate, which is to say associate, consecutive status messages 16 with each other based on the temporary radio identifier pID, so as to be able to determine, at least over a short period of time, the movement path (trajectory) of an OBU 10 based on the positions P, from consecutive status messages 16.

Onboard units 10 comprising safety applications 15 for sending such status messages 16 are defined in the ITS-G5 and WAVE (IEEE 802.11p) standards, for example. Status messages 16 of this type are referred to as common awareness messages (CAM) in the ITS-G5 standard and as basic safety messages (BSM) in the WAVE standard (notable SAE J2735). The temporary radio identifier pID of a status message 16 can, for example, be a temporary IP6 address, a MAC address or pseudo MAC address of the OBU 10, an exact or generalized geographical position (location coordinates) of the OBU 10, or the like. In the simplest case, the temporary radio identifier pID can thus even be identical to the position P, of the OBU 10.

The radio identifier pID is not known in the road toll system 1 or to the back office 2 and the radio beacons 3 and has no significance there; for example, it can also be randomly selected by an OBU 10. The radio identifier pID is also “temporary” in the sense that the same changes after a particular number of status messages 16 so as to suppress tracking of a particular OBU 10 over an extended period. For example, the radio identifier pID is changed after every fifth to thousandth, for example every twentieth to hundredth, status message 16. This method is shown in more detail in the sequence diagram of FIG. 3.

As an alternative, the radio identifier pID can be changed after a predetermined time period, or the change can be selectively omitted, which is to say suppressed by the onboard unit 10, while the same is present in the radio coverage range 4 of one and the same radio beacon 3. For this purpose, the onboard unit 10 can have previously stored information about the position of a radio beacon and/or the size of the radio coverage range 4, for example in the form of lists or maps, or have been notified thereof by a radio beacon 3, be it in the form of period broadcasts of a radio beacon 3 or as part of the messages 22, 27 and 27′ described below.

For the purpose of the method that is described here, the status messages 16 are modified as compared to conventional CAMs or BSMs in that these—instead of or in addition to the current position P_(i) of the OBU 10—in each case include the current relative distance A_(i) of the OBU 10 from a predetermined location 5-8. For this purpose, it is necessary for the OBU 10 to have information about the location coordinates (geographical position) P₀ of the predetermined location 5-8, for example of the point 5 or of the center or a reference point of the area 6, the boundary 7, the road segment 8, and the like.

The position information P₀ of the predetermined location 5-8 can, for example, have been previously stored in the OBU 10, for example in the form of a list, and more particularly the same have been stored during production or delivery of the OBU 10 or “on the fly”, for example received from one of the radio beacons 3, or distributed to the OBUs 10 by the back office 2 via the network of radio beacons 3 or another radio network, for example a mobile communication network. If several predetermined locations 5-8 exist, the OBU 10 transmits, for example in the status messages 16, the respective relative distance A_(i) from the nearest location 5-8, provided the OBU does not receive an order from a radio beacon 3, or in another manner, to calculate the relative distance A_(i) from another than the nearest location 5-8.

Calculating the relative distance A_(i) between the current position P_(i) of the OBU 10 and the position P₀ of the predetermined location 5-8 is a standard calculation of the length of the vector from P₀ to P_(i) according to the following equation

A _(i)=√{square root over ((X _(i) −X ₀)²+(Y _(i) −Y ₀)²+(Z_(i) −Z ₀)²)}{square root over ((X _(i) −X ₀)²+(Y _(i) −Y ₀)²+(Z_(i) −Z ₀)²)}{square root over ((X _(i) −X ₀)²+(Y _(i) −Y ₀)²+(Z_(i) −Z ₀)²)},   (1)

where (X_(i)/Y_(i)/Z_(i)) are the coordinates of the current position P_(i) of the OBU 10 and (X₀/Y₀/Z₀) are the coordinates of the position P₀ of the predetermined location 5-8. The calculation can, of course, also be carried out exclusively in the two-dimensional plane X/Y, which is to say the Z coordinates can be disregarded.

According to FIG. 3, the OBU 10 repeatedly transmits status messages 16, here denoted by CAM₁, CAM₂, CAM₃, . . . , or CAM_(i) in general. In the example shown, the radio identifier pID_(n) changes after the first three status messages 16, or CAM₁, CAM₂, CAM₃ from pID₁ to pID₂, and so forth. At the ith status message CAM_(i), the nth radio identifier pID_(n) is used (n<<i).

As a result, it is statistically very likely that two consecutive status messages 16 can be associated with each other based on the identical radio identifier pID_(i) thereof; it is only during the change of the radio identifier from pID_(n) to pID_(n+1) that a direct correlation of the status message 16 before and after the change of the radio identifier is not possible. In this case, a correlation of the status messages 16 is also possible by tracking the movement history of the onboard unit 10, for example by evaluating the speed thereof, directional vector thereof or the like, be it that this information is provided directly by the OBU 10 in the status messages 16 or measured by the radio beacon 3. It is also possible to store properties of the vehicle 9 that carries the OBU 10, such as the vehicle width, length, height or the like, in the OBU 10 and for the same to be conveyed in the status messages 16 or measured by the radio beacon 3, so as to increase the reliability of the correlation.

According to FIGS. 1 to 3, a radio beacon 3, which receives the status messages 16 of all OBUs 10 passing in the radio coverage range 4 thereof, is thus able to associate the status messages 16 originating from a particular OBU 10 with each other based on the radio identifiers pID and thus track the movement trend of the OBU 10 based on the relative distances A_(i), optionally also the entire trajectory of the OBU 10 based on the positions P_(i), if these are transmitted at the same time. For this purpose, the radio beacon 3 according to FIG. 2 comprises a processor 17, a transceiver 18 and an association process 19, which the processor 17 processes and which filters the flow of arriving status messages 16 with regard to correlating radio identifiers pID and feeds the relative distances A_(i) from mutually associated status messages 16 to a tracking process 20 that the processor 18 processes. If the radio identifiers pID directly correspond to the positions P_(i) or to geographical positions generalized therefrom, the association process 19 can also carry out the mutual association of the status messages 16 with each other based on a movement history (“tracking”) of the OBU 10.

The tracking process 20 compares the relative distances A_(i) thus obtained to a maximum distance a_(m) from a predetermined location 5-8, so as to detect a location usage. Moreover, the movement trend of the OBU 10 can be monitored for continually increasing or continually decreasing relative distances A_(i), so as to detect or suppress measurement outliers and reliably detect any occurrence where the distance limit a_(m) is exceeded.

In addition, the current positions P_(i), if these are transmitted at the same time, can be evaluated so as to further increase the detection reliability. Because the distance calculation according to equation 1 is carried out in the OBU 10, the tracking process 20 in the radio beacon 3 can be kept very simple and reduced, for example, to the simple comparison “A_(i)<a_(m)?”. Optionally, however, it is also possible to jointly evaluate multiple relative distances A, that are transmitted in consecutive status messages 16, for example form the mean value thereof and compare the same to the maximum distance a_(m).

If the predetermined location P₀ is a point 5, the location usage detected based on the relative distances A_(i) can additionally be validated when a predetermined number or a mean value of positions P_(i) drops below a maximum distance a_(m) from the point 5. If the location is an area 6, the detection of the location usage can additionally be validated when a predetermined number or a mean value of positions P_(i) is within the area 6. If the location is a road segment 8, the detection of the location usage can additionally be validated when, for example, the positions P_(i) indicate travel on the entire road segment 8, from the beginning thereof to the end thereof, or travel on a predetermined succession of multiple consecutive road segments 8 or the like. If the location is a boundary 7 (which incidentally can also be used to delimit the scope around the point 5, the area 6 or the road segment 8), the detection of the location usage can additionally be validated as a crossing of the boundary.

In a simplified embodiment, the radio beacon 3 can detect a location usage already from a single status message 16, so that the association process 19 can be eliminated. In this case, for example, a location usage can be detected when a single relative distance A_(i) drops below the maximum distance a_(m) around the point 5. If the status message 16 contains additional data, such as the speed and the movement direction, notably a movement vector M, of the OBU 10, usage of a location can also be detected when an extrapolation of the movement of the OBU 10 in the past or future shows that the unit just a moment ago used, is in the process of using, or will shortly use a location, for example has dropped below the maximum distance a_(m) or crossed or will cross the boundary 7.

As soon as the tracking process 20 detects a location usage, the process starts a service application 21 which is in charge of this location usage and which the processor 17 will process. The application 21 can, for example, be a logging, monitoring or authorization service, so as to record the detected location usage—identified for the OBU 10—or monitor the same, or authorize additional steps such as the opening of an access barrier, or the like. In the present example, the service application 21 is a tolling service that has the service identification sID and can impose tolls (charge fees) for the usage of the location by the OBU 10.

The service application 21 now transmits an identification request Id_Req 22, optionally together with the service identification sID thereof, via the transceiver 18 to the OBU 10 having the radio identifier pID that was indicated in the status messages 16 associated by the association process 19, refer also to FIG. 3. The identification request 22 may contain a cryptographic sender certificate “Cert” 23 of the radio beacon 3 so as to authenticate the same with respect to the onboard unit 10.

The OBU 10 addressed by way of the radio identifier pID receives the identification request 22 and forwards the same to the corresponding process, which here is the toll application 14. If the identification request 22 contains a sender certificate 23, the OBU 10 can check the authenticity of the certificate 23 in an optional step 24 (FIG. 3); if this certificate is authentic or valid, the remaining steps are carried out; if not, the identification request 22 is ignored.

The OBU 10 responds to the identification request 22 by releasing (disclosing) the identification uID thereof, which is unique throughout the system, which is to say consistently unique even over multiple changes of the radio identifier pID, see the declaration message Id_Rsp 25, which the unit returns to the transceiver 18 of the radio beacon 3 via the transceiver 13. The declaration message 25 may contain the service identifier sID of the polling service application 21 of the radio beacon 3, so that the declaration message can be supplied there to the correct service application 21.

From now on, the OBU 10 is identified with the unique identification uID thereof with respect to the service application 21, and the latter is identified with the service identifier sID and the certificate 23 thereof with respect to the OBU 10 or the toll application 14. Additional service-specific messages Svc_Msg 27 can now be exchanged between the transceiver 13 of the OBU 10 and the transceiver 18 of the radio beacon 3 via the radio interface 26. For example, the messages 27 can be service packs of a conventional toll log for tolling the usage of the location. The OBU identification uID can, for example, reference a toll account in the radio beacon 3 or the back office 2, which is debited the toll fees for the location usage. As an alternative, the identification uID could be compared to (at least) one legitimate (reference) identification uID_(ref) that was previously stored in the radio beacon 3 or the back office 2, wherein if identical the identification uID is authorized, for example, to access a location or receive a service.

As soon as the radio beacon 3 and the OBU 10 have been authenticated with respect to each other, in particular by evaluation of the sender certificate 23 of the radio beacon 3, all subsequent communication, such as the declaration message 25 and the ensuing service messages 27, can be transmitted in encrypted form via the radio interface 26, for example as encrypted point-to-point communication. Such an encrypted transmission channel could alternatively be established via a mobile communication network (not shown), instead of via the radio interface 26, for example directly with the back office 2.

In a simplified embodiment, in which the radio beacon 3 does not perform a tolling function, but is merely used to identify the vehicles 9 or OBUs 10, the determined identifications uID of the onboard units 10 can also simply be recorded—for example in each case together with a current time stamp t—in a memory 28 of the radio beacon 3 or back office 2 for logging purposes.

Following successful logging, authorization or tolling of a location usage, the radio beacon 3 can transmit a confirmation message “ok” to the OBU 10 in an optional step 27′ and transmit in this message (optionally again) a unique beacon identifier bID. The OBU 10 can store beacon identifiers bID received from radio beacons 3 and transmit at least the respective last beacon identifier bID received in one (or more) of the status messages 16 and/or in the disclosure of the identification uID thereof to a radio beacon 3 in step 25. The radio beacon 3 can thus ignore or suppress status messages 16 and/or identification transmissions 25, with which the same receives a beacon identifier bID that is identical to its own beacon identifier bID, so as to avoid double processing of one and the same passing OBU 10.

During the determination of the current positions P_(i) and the relative distances A_(i), the positions P_(i) of an OBU 10 can be improved by comparison to known reference positions—or at least to third-party positions that are subject to the same measurement errors—as is known from the field of differential GPS (dGPS). For example, the radio beacon 3 can have a dedicated satellite navigation receiver (not shown), which measures reference positions P_(ref,i) of the radio beacon 3 at approximately the same times at which the positions P_(i) are generated and makes these available, for example transmits these, to the OBU 10. Having knowledge of the previously known position of a stationary radio beacon 3, the positions P_(i) determined by way of satellite navigation can then be placed in relation to the reference positions P_(ref,i)—which are subject to approximately equivalent measurement errors—and measurement errors can thus be compensated for, refer to path 29 in FIG. 2. The respective positions P_(i) determined at similar times for neighboring OBUs 10 could be used in the same manner to correct the measurement errors of the positions P_(i) generated by an OBU 10 of interest.

Conclusion

The invention is not limited to the shown embodiments, but encompasses all variants and modifications that are covered by the scope of the accompanying claims. While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the embodiments. Thus, the breadth and scope of the described embodiments should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. 

What is claimed is:
 1. A method for identifying a vehicle using a predetermined location, comprising: carrying, on the vehicle, an onboard unit that via radio repeatedly broadcasts status messages, which each indicate a current relative distance of the onboard unit from the predetermined location and a radio identifier that changes after each or several status messages; receiving at least one status message in a radio beacon; detecting a location usage of the vehicle by evaluating the at least one status message based on the relative distance indicated therein; transmitting an identification request from the radio beacon to the onboard unit which is addressed by way of the radio identifier from the at least one status message; and receiving and conducting a legitimacy check of the identification request in the onboard unit and, if the request is legitimate, transmitting an identification of the onboard unit to the radio beacon, the identification remaining the same over several changes of radio identifier.
 2. The method according to claim 1, wherein information about the predetermined location is transmitted from the radio beacon to the onboard unit, which based on the information and based on the current position of the onboard unit calculates the relative distance.
 3. The method according to claim 1, wherein information about the predetermined location is stored in the onboard unit, which based on the information and based on the current position of the onboard unit calculates the relative distance.
 4. The method according to claim 1, wherein at least two status messages are received in a radio beacon and are associated with each other based on the radio identifiers indicated therein, and the location usage of the vehicle is detected by evaluating the mutually associated status messages based on the relative distances indicated therein.
 5. The method according to claim 1, wherein the legitimacy check is done by checking a cryptographic sender certificate of the radio beacon that is transmitted by the radio beacon along with the identification request.
 6. The method according to claim 1, wherein the identification of the onboard unit is transmitted to the radio beacon via an encrypted channel.
 7. The method according to claim 1, wherein the identification received in the radio beacon is recorded together with a time stamp in a memory so as to log the location usage, or is compared to at least one previously stored legitimate identification so as to authorize the location usage, or is used to search for and debit a toll account associated with the identification so as to toll the location usage.
 8. The method according to claim 7, wherein the radio beacon transmits a beacon identifier that is unique to the radio beacon to the onboard unit after logging, authorization or tolling of the location usage, the onboard unit storing the beacon identifier and transmitting the beacon identifier at least along with a subsequent broadcast of the status message(s) thereof or transmission of the identification thereof, and the radio beacon ignores a status message or identification received from an onboard unit if the beacon identifier received along therewith is identical to its own beacon identifier.
 9. The method according to claim 1, wherein the radio identifier is changed after every 20 to 100 status messages.
 10. The method according to claim 1, wherein the radio identifier is changed at the earliest after expiration of a predetermined time period.
 11. The method according to claim 1, wherein the radio identifier is kept the same while the onboard unit is present in the radio coverage range of the same radio beacon.
 12. The method according to claim 1, wherein each status message also indicates at least one of the current position or a current movement vector of the onboard unit, and said at least one is also used during the detection of the location usage.
 13. The method according to claim 1, wherein the current position of the onboard unit is determined by way of satellite navigation and is improved by referencing to a reference position of the radio beacon that was determined by way of satellite navigation.
 14. A radio beacon for identifying a vehicle using a predetermined location, the vehicle carrying an onboard unit that via radio repeatedly broadcasts status messages that each indicate a current relative distance of the onboard unit from the predetermined location and a radio identifier that changes after each or several status messages, the radio beacon configured to, with the aid of a processor and a transceiver connected thereto, receive at least one status message; detect a location usage by evaluating the at least one status message based on the relative distance indicated therein; transmit an identification request to that onboard unit which is addressed by way of the radio identifier from the at least one status message; and receive an identification of the onboard unit that remains the same over several radio identifier changes.
 15. An onboard unit, comprising a processor, a satellite navigation receiver for position determination, and a transceiver for radio communication, wherein the onboard unit is configured to, with the aid of the transceiver, repeatedly broadcast via radio status messages, which each contain a radio identifier of the onboard unit that changes after several status changes, wherein the onboard unit is further configured to indicate in each status message a current relative distance from a predetermined location, as determined by way of the satellite navigation receiver, the onboard unit further configured to receive, from a radio beacon, an identification request that is addressed to the current radio identifier of the unit and contains a cryptographic sender certificate; validate the sender certificate; and if the sender certificate is valid, transmit an identification of the onboard unit to the radio beacon, the identification remaining the same over several changes of radio identifier. 